The present invention relates to a two-phase/four-phase modulated spread spectrum communication system with a comb-form spectrum which is designed so as to reduce co-channel interference.
The present applicant has announced an approximately synchronized CDMA system that uses signals consisting of pseudo-periodic sequences as a signal design method which makes it possible to avoid no co-channel interference.
In this signal design method, interference between desired and undesired channels can be eliminated; as a result, the signal of a desired channel can be efficiently separated from the other undesired channels. However, in conventional approximately synchronized CDMA systems, signals are designed by using multi-phase sequences; consequently, the signals on respective channels are not two-phase signals (which are signals expressed by +, xe2x88x92) or four-phase signals (which are signals expressed by +, xe2x88x92, j, xe2x88x92j), and therefore, they should be made of much more complicated communication equipment.
The present invention was devised in light of the above facts; and in claim 1, the object of the present invention is to provide a two-phase/four-phase modulated spread spectrum communication system with a comb-form spectrum which makes it possible to simplify the construction of a communication equipment by means of two-phase signals or four-phase signals.
Furthermore, in claim 2, the object of the present invention is to provide a two-phase/four-phase modulated spread spectrum communication system with a comb-form spectrum which makes it possible to assign different carrier waves to respective users by means of two-phase signals or four-phase signals.
Furthermore, in claim 3, the object of the present invention is to provide a two-phase/four-phase modulated spread spectrum communication system with a comb-form spectrum which makes it possible, using two-phase signals or four-phase signals, to prevent the generation of side lobes in the vicinity of the main pulses in signals produced from the matched filter on the reception side.
Furthermore, in claim 4, the object of the present invention is to provide a two-phase/four-phase modulated spread spectrum communication system with a comb-form spectrum which makes it possible to create a plurality of code words by the use of two-phase signals or four-phase signals.
In order to accomplish the above-described objects, in claim 1, the two-phase/four-phase modulated spread spectrum communication system with a comb-form spectrum of the present invention is characterized by the fact that a basic sequence consisting of two-phase or four-phase chips is prepared, and an extended transmission frame is constructed by repeating one or a plurality of the basic sequence so as to obtain a periodic sequence of finite length with a comb-form spectrum and by duplicating and adding one or a plurality of chips of the back portion and front portion of the periodic sequence of finite length to the outside of the front portion and outside of the back portion of the periodic sequence of finite length; and on the reception side the extended transmission frame is demodulated using a matched filter which is matched with the periodic sequence of finite length prior to extension.
Furthermore, in claim 2, the present invention is characterized by the fact that in the two-phase/four-phase modulated spread spectrum communication system with a comb-form modulated spectrum claimed in claim 1, different carrier waves are assigned to respective users, and two-phase signals or four-phase signals with a comb-form modulated spectrum are assigned to the respective carrier waves thus assigned.
In addition, in claim 3, the present invention is characterized by the fact that in the two-phase/four-phase modulated spread spectrum communication system with a comb-form modulated spectrum claimed in claim 1 or 2, the basic sequence is formed as a two-phase or four-phase orthogonal sequence or as a multi-phase orthogonal sequence, and side lobes are prevented from being generated in the vicinity of the main pulses produced from the matched filter on the reception side, thus reinforcing the anti-multi-path characteristics.
Furthermore, in claim 4, the present invention is characterized by the fact that in the two-phase/four-phase modulated spread spectrum communication system with a comb-form modulated spectrum claimed in claim 1, a plurality of different types of the extended transmission frame are prepared so as to be used as code words.